The present invention relates to an electronic control apparatus, including microcomputers, for controlling some of the systems found in a vehicle, including the engine and transmission mechanism.
As is known, an electronic control apparatus with a one-chip microcomputer is used in a vehicle to control the fuel injection and the ignition timing. The engine conditions are monitored, and from the detected conditions the microcomputer calculates both the proper amount of fuel to be injected and the proper ignition timing. The calculated amount of fuel is then injected into the cylinders of the engine and ignited at the calculated time, thus controlling the engine. A variety of sensors for monitoring the conditions of engines are known. Among them are: an intake airflow sensor, a cooling water temperature sensor, an engine speed sensor, a throttle valve opening sensor and a sensor for detecting the oxygen content in the exhaust gas. The output signals of these sensors are supplied to the one-chip microcomputer. The microcomputer reads data from memories in accordance with the data received from the sensors. It then processes the data, calculating a proper amount of fuel to inject and an appropriate ignition timing.
Not only the engine, but the automatic transmission mechanism, constant speed control mechanism, brake mechanism and other mechanisms of the vehicle must also be controlled. To control the engine and these mechanisms, a great amount of data must be input to the one-chip microcomputer. The microcomputer must process the data according to a very large program and, itself, must output a great amount of data. It needs a large number of input/output (I/O) ports. A one-chip microcomputer alone cannot process so much data and, hence, cannot control the engine or the mechanisms mentioned above.
In view of this, an electronic control apparatus for use in vehicles must comprise two or more one-chip microcomputers. The control system of the apparatus will, unavoidably, be very complex since the microcomputers must operate independently.